The present invention relates to a driving method, a measurement method and a measurement apparatus of a solid state image pickup device.
A solid state image pickup device is widely used as an image pickup means in a variety of cameras such as electronic still cameras, home video cameras and various business video cameras including broadcasting station cameras. Demanded characteristics and demanded performance of a camera vary from application to application. Nevertheless, there is no difference from semiconductor devices of other types in that it is necessary to measure and evaluate a solid state image pickup device in order to form a judgment as to whether or not the solid state image pickup device has the required characteristics and the required performance. In addition, there is a large number of characteristics that need to be measured and evaluated. For example, levels of various dark signals.are specially important characteristics that need to be measured and evaluated.
In the conventional measurement of a solid state image pickup device, when the measurement of an item of measurement is completed, the measurement of a next item of measurement is started. In the conventional measurement, a result of measurement is thus found for each item of measurement of the solid state image pickup device which is measured with timing different from item to item. A variety of measurement results are then processed to find characteristics of another item or another kind.
As an example, the following description explains the conventional general method of measurement and evaluation of the level of a dark signal in a CCD solid state image pickup device. A dark signal of the CCD solid state image pickup device is measured with the device driven by using the ordinary driving method to operate in a state of being shielded from light to read out data from a frame or a field. Then, a dark signal generated by portions of the CCD solid state image pickup device other than a sensor unit (that is, an image pickup area) is measured by putting the device in a state allowing an operation to read out data with a supply of particular read pulses halted. Examples of the portions other than the image pickup area are vertical and horizontal registers. Finally, an output of the read operation with a supply of particular read pulses halted is subtracted from an output of the read operation driven by using the ordinary driving method in a state of being shielded from light in order to find a dark signal generated by the sensor unit.
By the way, in the conventional measurement method described above whereby a result of measurement is found for each item of measurement of a solid state image pickup device measured with timing different from item to item and a variety of measurement results are then processed to find characteristics of another item or another kind, a manual operation is required each time a driving condition is changed, giving rise to a problem that the measurement work is cumbersome and that it takes a long time to complete the measurements.
In addition, there is also raised a problem that, since the magnitude of the dark signal itself is typically small and variations in magnitude due to changes in temperature are relatively big, the measurement is prone to big errors caused by changes in measurement conditions which are attributed to the changes in temperature. For example, a dark signal of portions other than the sensor unit is normally measured after a period of time has lapsed since the measurement of a completely dark signal. If the temperature changes during the period of time, the change in temperature will cause a big error in a dark signal of the sensor unit which is found by subtracting the dark signal generated by the portions other than the sensor unit from the completely dark signal.
It is thus an object of the present invention addressing the problems described above to make the measurement of a solid state image pickup device easy to carry out, to shorten the measurement time and to improve the measurement accuracy.
The present invention is characterized in that the solid state image pickup device is operated to generate an output with an operating condition for an odd field made different from that for an even field or, in other words, such an operation of the solid state image pickup device is a characteristic of the present invention.
As a result, according to the present invention, it is possible to obtain information on a variety of characteristics of a solid state image pickup device or to measure the characteristics at the same time in a state with different operating conditions applied such as a playback state.
In particular, a dark signal can be detected with the supply of read pulses for either odd or even fields halted typically at the same time as a playback signal is detected in a state of being shielded from light or a state of applying an incident light with a predetermined quantity. It is thus possible not only to measure a variety of characteristics merely under a plurality of conditions at the same time but also to further process outputs of the odd and even fields in order to measure still another characteristic such as a dark current generated by an image pickup area.
As described above, the present invention is characterized in that the solid state image pickup device is operated to generate an output with an operating condition for an odd field made different from that for an even field or, in other words, such an operation of the solid state image pickup device is a characteristic of the present invention. A CCD solid state image pickup device is a typical solid state image pickup device to which the present invention is applied. It should be noted, however, that the scope of the present invention is not limited to such a CCD solid state image pickup device. That is to say, the present invention can also be applied to any solid state image pickup device as long as the device is capable of carrying out interlace operations. Examples of devices to which the present invention can be applied are a MOS solid state image pickup device and an amplification type solid state image pickup device. As for the CCD solid state image pickup device, the present invention can be applied to both the interline and interframe types. In addition, the present invention can also be applied to an image pickup device wherein an array of sensors such as linear sensors is divided into 2 portions allocated to odd field pixels and even field pixels and data is read out from both the portions.
In the most typical technique of making an operating condition for an odd field made different from that for an even field, an operation to read out pixel data from either the odd or even field to a vertical register is halted. It should be noted, however, that the scope of the method provided by the present invention is not limited to such a technique. For example, the frequencies of driving pulse signals for the odd and even fields, that is, the horizontal transfer pulse signal and the vertical transfer pulse signal, are made different from each other and the amount of unnecessary radiation at one of the frequencies is measured.